1- Thickness 0.005" 2- I usually reduce 50% of the thermal pad, but it also depend on original size of thermal pad somehow I have to either create window panel or crosshatch otherwise component wil get wimming during reflow. Hope this will help.

A reduction along with cross hatching is a must for the center pad to reduce paste volume as well as to assure even paste deposit while printing on a large pad. With out the cross hatch, the squeegie will most likely pull paste away from the center of the large ground pad.